Electrolytic metal deposition is a widely used industrial process having application to a wide variety of products and fields. In electronic applications where a specific metal pattern is required, electrolytic deposition may be used in either of two manners. In the first, a uniform metal layer is formed by electrolytic deposition, the exposed surface of that layer is coated with a photoresist, the photoresist is then exposed in the desired pattern for the final metal structure, the photoresist is developed and the structure is etched to remove the unprotected electroplated material In the second technique, a photoresist pattern is disposed on the conductive surface of a substrate structure, exposed and developed to expose the underlying conductive layer in the desired plating pattern. Thereafter, the structure is electroplated to produce a thick layer on the exposed portion of the underlying conductive layer. Where relatively thick conductive layers are desired, these processes both present problems with respect to the durability of the photoresist in the etching or plating bath because extended time periods in these solutions can cause deterioration of the photoresist. Sufficient deterioration of the photoresist results in plating or etching in undesired locations. Another technique for plating which can be used for a connected structure is to define the conductor to be plated with photoresist and remove the rest of the layer. This process depends on carrying the plating current through the structure being plated itself This tends to result in non-uniform plating with the greater thickness being near the external electrical connections to the structure and successively lesser thicknesses further from the connections. Thus, this is not a preferred method. An additional problem where fine line, thick metallic patterns are desired is the inability of both the plating-followed-by-photoresist-and-etching and the photoresist-followed-by-plating process to provide reliable definition of fine line structures. Another problem with the plating followed by photoresist and etching process is the problem of accurately aligning the photoresist exposure mask with respect to the underlying structure on the substrate beneath a thick metal layer.
There is a need for a process which enables thick, patterned layers of metal to be electrolytically deposited on a conductive substrate in a reliable manner with a minimum of processing steps.